A substantial proportion of cancers could be prevented. All cancers caused by tobacco use and heavy alcohol consumption could be prevented completely. In 2015, almost 171,000 of the estimated 589,430 cancer deaths in the US will be caused by tobacco smoking. In addition, the World Cancer Research Fund has estimated that up to one-third of the cancer cases that occur in economically developed countries like the US are related to overweight or obesity, physical inactivity, and/or poor nutrition, and thus could also be prevented.
Certain cancers are related to infectious agents, such as human papillomavirus (HPV), hepatitis B virus (HBV), hepatitis C virus (HCV), human immunodeficiency virus (HIV), and Helicobacter pylori (H. pylori). Many of these cancers could be avoided by preventing infection, either through behavioral changes or vaccination, or by treating the infection. Many of the more than 3 million skin cancer cases that are diagnosed annually could be prevented by protecting skin from excessive sun exposure and avoiding indoor tanning.
Screening can prevent colorectal and cervical cancers by allow- ing for the detection and removal of precancerous lesions. Screening also offers the opportunity to detect cancer early, before symptoms appear, which usually results in less extensive treatment and better outcomes. Screening is known to reduce mortality for cancers of the breast, colon, rectum, cervix, and lung (among long-term and/or heavy smokers). A heightened awareness of changes in the breast, skin, or testicles may also result in the early detection of cancer.
The 5-year relative survival rate for all cancers diagnosed in 2004-2010 was 68%, up from 49% in 1975-1977. The improvement in survival reflects both the earlier diagnosis of certain cancers and improvements in treatment. Survival statistics vary greatly by cancer type and stage at diagnosis. Relative survival is the percentage of people who are alive a designated time period after a cancer diagnosis (usually 5 years) divided by the percentage expected to be alive in the absence of cancer based on normal life expectancy.
It does not distinguish between patients who have no evidence of cancer and those who have relapsed or are still in treatment. While 5-year relative survival is useful in monitoring progress in the early detection and treatment of cancer, it does not represent the proportion of people who are cured because cancer deaths can occur beyond 5 years after diagnosis. In addition, although relative survival provides some indication about the average survival experience of cancer patients in a given population, it may not predict individual prognosis and should be interpreted with caution. First, because 5-year relative survival rates for the most recent time period are based on patients who were diagnosed from 2004 to 2010, they do not reflect the most recent advances in detection and treatment. Second, factors that influence individual survival, such as treatment protocols, other illnesses, and biological or behavioral differences in cancers or people, cannot be taken into account.
Third, survival rates may be misleading for cancers detected before symptoms arise if early di-agnosis does not extend lifespan. This occurs when cancer is diagnosed that would have gone undetected in the absence of screening (over-diagnosis) or when early diagnosis does not alter the course of disease. In other words, increased time living after a cancer diagnosis does not al-ways translate into progress against cancer.